Why the large discrepancies between the Ipsos poll and Gallup Party-ID survey?

The Ipsos poll also indicated a Party_ID split of 36% Democrats and 25% Republicans – an apparent contradiction to the polling sample. Assuming the other 39% were Independents, it is a close match to the Gallup Survey.

In the primaries, Sanders won approximately 65% of Independents and 35% of Democrats. One would logically expect that Stein would do nearly as well as Sanders against Clinton in a four-way race. They are in essential agreement on major issues – and Clinton has very low approval ratings. But Stein had an implausibly low 3% on Aug. 24 and 1% on July 17.

True Vote Model Model Base Case

This is not a forecast. It is a scenario analysis based on the following assumptions.

Party-ID: 39% Independents, 36% Democrats, 25% Republicans. Vote shares: Stein has 40% of Independents and 35% of Democrats. Clinton has 25% and 50%, respectively. They each have 5% of Republicans.